Motor-driven hydraulic power steering apparatuses are conventionally known which are adapted to rotate an oil pump by an electric motor and supply a working oil to a power cylinder from the oil pump to mitigate an operation force required for operating a steering wheel.
In a power steering apparatus of this type, the electric motor is generally driven to provide steering assist only when the steering operation is performed.
The power steering apparatus is provided with means for inputting a temperature detection signal indicative of the temperature of a motor driver element to protect the driver element.
Since an oil-cooling system is typically employed for cooling the driver element, it is expected that there is a certain relationship between the temperature of the driver element and the temperature of the oil. If the oil temperature can be estimated on the basis of the temperature of the driver element, the determination of the oil temperature can be achieved without the provision of an oil temperature sensor.
Where a plurality of motor driver elements are provided, the respective elements have different temperature increase rates and, therefore, a temperature sensor is attached to each of the elements. Accordingly, a plurality of temperature sensors are required, thereby complicating the construction of the power steering apparatus.